The present invention relates to a print-termination detecting method and apparatus for a line printer of a type employing a character carrier, such as a character band, which continuously moves along a print line.
As is well known, such a line printer is configured so that printing is carried out by alternately repeating a printing cycle and a paper feeding cycle including a data receiving cycle for receiving print data and paper-feed data. In the printing cycle, a comparing operation is carried out to judge whether or not a character on a character carrier agrees with a print datum according to which a print hammer column is to perform printing. When the character accords with the print datum, a print hammer on a column corresponding to the print datum is driven to perform printing. In general, the printing speed may be increased if both the printing cycle and the paper feeding cycle are shortened. However, current designs have reached a limitation so that it is difficult to further shorten those cycles. Accordingly, further improvements in printing speed cannot be expected merely by increasing the printing cycle and the paper feeding cycle.
To obtain yet further improvements, there has been proposed, as disclosed, for example, in commonly assigned Japanese Patent Examined Patent Publication No. 61-38037, a printer in which, based on the fact that a dead time exists between the time of issuing a paper feeding instruction and the time of actually starting the motion of paper, a paper feeding instruction is issued immediately before the termination of printing cycle to thereby shorten the paper feeding cycle. Such a printer in shown in FIG. 2.
According to this proposal, a paper feeding instruction is based issued on an estimation that the printing cycle is finished when a comparing operation has been repeated a predetermined number of times. However, such estimation often becomes impossible when the pattern of print data changes. Further, such estimation becomes invalid when a parity error or the like occurs. Consequently, there are a large number of drawbacks in practical use.